Abstract
The ionospheric weather is affected not only from above by the Sun but also from below by processes in the lower-lying atmospheric layers. One of the most pronounced atmospheric phenomena is the sudden stratospheric warming (SSW). Three major SSW events from the periods of very low solar activity during January 2009, February 2018, and December 2018/January 2019 were studied to evaluate this effect of the neutral atmosphere on the thermosphere and the ionosphere. The main question is to what extent the ionosphere responds to the SSW events with focus on middle latitudes over Europe. The source of the ionospheric data was ground-based measurements by Digisondes, and the total electron content (TEC). In all three events, the ionospheric response was demonstrated as an increase in electron density around the peak height of the F2 region, in TEC, and presence of wave activity. We presume that neutral atmosphere forcing and geomagnetic activity contributed differently in individual events. The ionospheric response during SSW 2009 was predominantly influenced by the neutral lower atmosphere. The ionospheric changes observed during 2018 and 2018/2019 SSWs are a combination of both geomagnetic and SSW forcing. The ionospheric response to geomagnetic forcing was noticeably lower during time intervals outside of SSWs.
Highlights
The Earth’s ionosphere is created by solar-ionizing EUV and X-ray radiation and energetic particle precipitation.The term space weather refers to conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and that can affect human life and health
Limited number of papers has been studying ionospheric effects of stratospheric warming (SSW) at middle latitudes compared to low latitudes
We observed significant ionospheric short-time changes for all three studied SSW events, and all of them exhibited an increase in the plasma frequency on days of maxima of stratospheric temperature or very close to them, partly in coincidence with the reversed zonal wind that defines the occurrence of major SSW, as well
Summary
The Earth’s ionosphere is created by solar-ionizing EUV and X-ray radiation and energetic particle precipitation. Model EAGLE (entire atmosphere global model) shows that the phase change of SW2 in the neutral wind caused by the 2009 SSW at the altitude of the dynamo electric field generation had a crucial importance for the observed lowlatitudinal TEC disturbances [24]. The decrease in F2 region electron density was explained as change in ratio between O and N2 as well as change in zonal electric field They observed decrease in foF2 on days corresponding to maximal positive disturbance in stratospheric temperature. The ionosphere is heavily affected by the geomagnetic activity, which is reflected in the electron concentration profile changes, most visibly in the F region Both ionospheric density increase as well as decrease can occur during a magnetic storm in middle latitudes; they are called ionospheric positive and negative storms, respectively. Both described mechanisms (negative and positive storm) can serve as basic descriptions of the observed electron density changes during geomagnetic storms; many further issues can complicate the effect on the ionosphere [39]
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